The present invention generally relates to a thin film EL panel which is adapted to emit its light in response to the application of an electric field so as to make it possible to correspondingly display multicolor.
Conventionally a thin film EL panel is constructed as shown in FIG. 6. The thin film EL panel has a transparent electrode 62, an insulating layer 63, a light emitting layer 64, an insulating layer 65, and a transparent electrode, 66 on the rear face side, respectively formed on a glass base plate 61. As a transparent electrode 62 has higher melting point than 660.degree. C., the above described transparent electrode 62 can endure the thermal process in the above described forming step. In order to avoid heat to be caused in the manufacturing process, a color filter 67 which has a pattern corresponding to the picture element in a region with the above described transparent electrode 62 and the transparent electrode 66 on the rear face side being opposed is formed on a color filter forming base plate 68 provided above the transparent electrode 66 on the above described rear face side. Upon the application of the field between the above described transparent electrode 62 and the transparent electrode 66 on the rear face side, the above described thin film EL panel emits its light in the above described light emitting layer 64. The above described thin film EL panel transmits through a color filter, the light to be generated by the above described light emitting layer 64 so as to display multicolor.
Another thin film EL panel is provided with an Al electrode, instead of a transparent electrode 62 as described in the above-mentioned thin film EL panel shown in FIG. 6.
The former thin film EL panel has problems in that the electrode is formed as an electrode closer to the glass base plate 61 having a melting point higher than 660.degree. C. Further, resistance and consumption power of the transparent electrode 62 are larger, respectively. The thin film EL panel is formed on the rear side from the side where the light is taken out, and thus is not required to be transparent. Further, as the above described transparent electrode 62 is transparent as an electrode closer to the base plate which is an electrode desired to be higher in the reflection factor of the light, the reflection factor of the light of the transparent electrode 62 is lower, and the light takeout efficiency becomes lower. As compared with a case of using the Al electrode, the light emitting efficiency becomes approximately half as low, which is a problem.
When a light emitting layer is generally formed by an electronic beam evaporating method in the manufacturing step of the thin film EL panel, the thermal treatment is affected at the temperatures of 550.degree. C. or more after the formation of the light emitting layer. When the light emitting layer is formed by a CVD (chemical.vapor. deposition) method including ALE (atomic.layer.epitaxy), the temperature of the base plate becomes 500.degree. or more. The thermal process in these manufacturing steps is unavoidable so as to obtain the light emission efficiency for practical use. The electrode close to the above described basic plate cannot avoid the influences of the thermal process in the manufacturing step of the insulating layer and the light emitting layer after the formation of the electrode.
As the above described Al electrode as an electrode closer to the base plate does not have a melting point higher than 660.degree. C. in the thin film EL panel of the latter, there is a problem in that the above described Al electrode is deteriorated by the thermal process in the above described manufacturing step. Generally, the melting point of the Al is 660.degree. C. In the case of Al of the thin film as in the Al electrode to be used in the thin film EL panel, the Al of the above described thin film is increased in the ratio of the surface energy so as to lower the melting point. The melting point of the Al electrode of the film thickness 1000 .ANG. formed on, for example, the glass base plate becomes 630.degree. C. or lower. When an insulating layer has been formed by a sputtering method on the above described Al electrode, the melting point of the above described Al electrode is further lowered. When the film thickness of the above described Al electrode has been made 5000A or more, the above described Al electrode can endure the thermal process of a temperature of 550.degree. C. When the film thickness of the above described Al electrode, which is an electrode in the ground work closer to the glass base plate, becomes thicker in the thin film EL panel, problems such as insulating destruction and so on are caused due to the pattern edge of the Al electrode. This therefore makes it difficult to make the film of the above described Al thicker. Also, as the above described Al electrode is likely to cause havoc even in the comparatively cold temperature of the melting point or lower of the Al electrode, there is a problem in that it is difficult to retain a high quality light emission while maintaining the flatness property of the above described Al electrode. Further, as the oxidizing force of the Al is strong, there is a problem in that the above described Al electrode and the parts to come into contact with the above described Al electrode are likely to be chemically deteriorated. Thus, the high quality of light emission becomes difficult to keep.